The present invention relates to a coating type reinforcement composition of sheet metal, and more particularly a reinforcement composition of a thermosetting epoxy resin which can be applied under warming for ensuring satisfactory levels of tensile rigidity and resistance to dent of a thin sheet metal mainly due to weight reduction of an automobile body, or for collision safety, and which particularly improve a bending strength and a rigidity of the sheet metal without causing a distortion to the sheet metal by blending an inorganic filler of a particular aspect ratio (L/D), as well as a reinforced sheet metal structure using the reinforcement composition, and a reinforcing method of a sheet metal for an automobile body.
As this kind of a reinforcement of a sheet metal for an automobile body, for example, a thermosetting epoxy resin sheet cut to an appropriate size without or with a restraint layer (e.g., glass cloth or aluminum foil, etc.) laminated on the upper side of the thermosetting epoxy resin sheet and optionally a release paper for prevention of blocking (sticking) provided on the underside of the thermosetting epoxy resin sheet has been greatly used.
Such sheet-type reinforcement (the present type) may be bonded to a predetermined area of the sheet metal and subjected to heat-curing under the baking conditions (typically at 150 to 200xc2x0 C.) in an electrodeposition furnace in the painting step of automobile manufacturing line to show a reinforcing effect as desired.
However, said application of the reinforcement depended on a human work and the automating thereof was very difficult, which led to the low productivity. In case of omitting the restraint layer, the sheet metal may be distorted due to shrinkage resulting from heat-curing when the thermosetting epoxy resin is designed to have an elastic modulus suitable for obtaining a desired level of reinforcing effect. Further, the cost for disposal of the release paper may not be disregarded.
Under such a circumstances, a great effort has been made to develop a coating type reinforcement composition that can be automatically applied in bead spray or band shape from nozzle for the purpose of increasing the productivity. For example, a composition of a thermosetting epoxy resin blended with a particular placticizer and acrylic powder having a particle diameter of 0.1 to 50 xcexcm is known (referred to Japanese Patent Laid-Open Publication No. 302278/1996). However, this coating type reinforcement composition required heat treatment at 100 to 200xc2x0 C. for 5 to 180 seconds immediately after application. Further, a placticizer and acrylic powder were blended with an epoxy resin as described above and an elastic modulus is set to a degree of inhibiting an occurrence of distortion in the sheet metal reinforced by the cured composition. Moreover, the composition had a disadvantage that if its elastic modulus is designed to obtain a desirable level of reinforcing effect, it may cause distortion in the sheet metal in the same way as said present type without a restraint layer.
The present inventors, after intense studies to overcome the above-described problems of such a coating type reinforcement, developed the present invention based on the findings that a viscous composition with a high viscosity comprising a liquid component of thermosetting epoxy resin blended with an inorganic filler of a particular aspect ratio (L/D) can be applied under warming; and by leaving it to cool to a solidification after applying, its scatter, dissolution or omission is not occurred particularly to a shower-resistance and a chemical conversion treatment or electrodeposition solution until the curing/baking step; also in the reinforcing effect, the bending strength and the rigidity of the sheet metal are improved, and the generation of distortion in the sheet metal is prevented after curing.
Accordingly, the present invention provides a coating type reinforcement composition of sheet metal which comprises a liquid epoxy resin, a latent curing agent and an inorganic filler of an aspect ratio (L/D) of 5 or higher, an amount of said inorganic filler contained being 20 to 50% by weight and being a viscous composition with a high viscosity.
In addition, the present invention also provides a reinforced sheet metal which comprises a sheet metal of an automobile body provide with a reinforcement layer obtained by applying said coating type reinforcement composition of sheet metal to the sheet metal and allowing to heat cure; and
a reinforcing method of a sheet metal for an automobile body which comprises in automobile manufacturing line, applying said coating type reinforcement composition of sheet metal under warming to a sheet metal which has been press-shaped during the body-making step or those after assembling thereof; passing the coated sheet metal through the pre-treatment and electrodeposition coating steps in the state of leaving it to cool and solidify; and heat-curing under the baking conditions in an electrodeposition furnace during said electrodeposition coating step to form a reinforcement layer.